Facial masks are well known for use in continuous positive airway pressure (CPAP) treatment of various respiratory ailments and sleep disordered breathing (SDB), such as, for example, obstructive sleep apnea (OSA) and/or other ventilatory assistance treatments such as noninvasive positive pressure ventilation (NPPV). See, for example, U.S. Pat. No. 4,944,210, the entire content of which is expressly incorporated hereinto by reference. While the present invention will be described below with reference to a full facial mask for use in CPAP treatment, it will be understood that such a reference is non-limiting and is directed toward a particularly preferred embodiment of the present invention. Thus, the various characteristics and advantages of the present invention could equivalently be embodied in another type of mask, such as a nasal mask, or another type of NPPV therapy.
Apparatus for the treatment of SDB generally involves a blower which delivers a supply of air at positive pressure to a patient interface via a conduit. The patient interface may take several forms, such as a nasal mask assembly and a nasal and mouth mask assembly (i.e., a full face mask). Patients typically wear a mask assembly while sleeping to receive the NPPV therapy.
Mask assemblies typically include a rigid shell or frame and a soft face-contacting cushion. The cushion cushions the rigid frame from the patient's face, and provides a seal with the patient's face. The frame and cushion define a cavity which receives the nose or nose and mouth. The frame and cushion are held in position on the patient's face by a headgear assembly. The headgear assembly typically comprises an arrangement of straps which pass along both sides of the patient's face to the back or crown of the patient's head.
One problem that arises with existing masks used for CPAP treatments is that over-tightening of the mask straps results in compression of the mask against the wearer's face which may therefore apply undue pressure force against certain of the wearer's facial features, such as the wearer's nose. A poorly fitting mask can leak when pressurized which encourages a patient to tighten the headgear straps excessively which, in turn leads to discomfort, marks on the face and in some cases facial sores.
The cushion of a patient mask interface can play a key role in the comfort and effectiveness of therapy. The nasal bridge area of the patient's face has been identified as being particularly sensitive and thus a mask design needs to pay particular attention to such region.
The issue of mask comfort and effectiveness is particularly apparent when treatment pressure varies, for example, when a patient uses an automatic positive airway pressure (APAP) device such as those commercially available from ResMed Limited under the tradename AUTOSET. When the pressure varies, patients may set the headgear tension for the highest pressure, which thereby leads to unnecessarily high tension being experienced at lower pressures.
To address such problems, mask systems that vary the sealing force with treatment pressure have been developed, including a nasal mask cushion having a gusset portion, as evidenced by U.S. Published Patent Application 2002/0029780; U.S. Pat. No. 6,772,760 and U.S. Published Patent Application US 2004/0118406, the entire content of each being expressly incorporated hereinto by reference. A commercial embodiment of the inventions described in such patent publications is the ACTIVA™ mask system available from ResMed Limited.
U.S. Pat. No. 5,074,297 (the entire content of which is expressly incorporated hereinto by reference) describes a respiratory mask assembly for use with intermittent positive pressure breathing treatment and is said to facilitate the formation and automatic adjustment of the seal between a patient's face and a facial unit of the respiratory mask.
While the prior proposals for adjustable mask cushions may be satisfactory for their intended purposes, improvements are still needed, especially for a full face mask patient interface.